Arroyo (10-8), who shut out the New York Mets on four hits in previous start, allowed five hits and struck out six over seven innings Friday.
Arthur Rhodes came on to work a perfect eighth and Francisco Cordero allowed a hit and struck out one during the ninth in a non-save situation.
Encarnacion, who went 3-for-3 in the series opener Thursday, went 4-for-4 Friday.
He had an RBI single during Cincinnati's two-run fifth and added a solo homer in the eighth.
The Reds ended a three-game losing streak and won for only the third time in 10 games.
Jeff Suppan (5-7) took the loss, although all three runs he allowed were unearned.
Copyright 2009 by United Press International.